1. Field of the Invention
The present invention relates to satellite power systems. In particular, the present invention relates to a satellite power system employing bilateral battery charging and single set point control.
2. Description of Related Art
Power converters are well known and have been used to charge and discharge batteries. Examples of such power converters are disclosed in U.S. Pat. Nos. 4,347,474; 4,549,254; 4,672,303; 4,729,088; and 4,947,311. However, these power converters as well as other power converters in the art are not suited for use in satellites.
FIG. 1 illustrates a battery charge/discharge configuration known in the prior art. The circuit of FIG. 1 includes separate circuits for charging and discharging the battery. The charge and discharge circuits each have their own controller. The interaction of the charge and discharge circuits is controlled by steering logic that is coupled to the charge controller and the discharge controller. A particular problem with the prior art is the need for this additional steering logic to control the operation of the charge and discharge circuits. The steering logic can be very complex and also is an area of possible instability due to the interaction between the charge and discharge circuits.
Another problem with the designs of the prior art is their weight. For converters used in satellites, weight is a primary consideration because of the tremendous launch and payload costs for spacecraft. The battery charge/discharge circuit of FIG. 1 is particularly a problem since separate circuits are required to perform the charging and discharging functions; thus, the power converters add to the weight of the satellite.
A further problem with the converters of the prior art is reliability. Since the power converters will be used in satellites, they will not be easily accessible once placed in operation. Thus, separate controlling circuits and complex steering logic are areas were the converters are likely to malfunction. This tends to reduced the reliability of the entire satellite.
U.S. Pat. Nos. 4,736,151 and 4,801,859 issued to Dischner disclose a bi-directional converter, These converters are designed to operate in an electrically-compensated constant speed drive. The control of the converter is not continuous. One switch is held off while the other switch is pulse width modulated. Additionally, the converter of Dischner produces a discontinuity at zero power flow that is detrimental to power charging/discharging systems. Thus, the converters of Dischner would not be suitable for satellite applications.